[fix] Fixed failing QA check openwisp#467

The QA check was failing earlier because the latest commit wasn't
following the conventional commit guidelines, this commit fixes it. Ran
both the openwisp-qa-format and openwisp-qa-check commands.

Fixes openwisp#467

openwisp_radius/api/serializers.py

@@ -120,7 +120,9 @@ class RadiusPostAuthSerializer(serializers.ModelSerializer):
         allow_blank=True,
         style={'input_type': 'password'},
     )
-    called_station_id = serializers.CharField(required=False, allow_blank=True, max_length=50)
+    called_station_id = serializers.CharField(
+        required=False, allow_blank=True, max_length=50
+    )
     calling_station_id = serializers.CharField(required=False, allow_blank=True)
 
     def validate(self, data):